This invention relates to capturing and processing the full bandwidth of an Ultra-Wideband (UWB) signal and especially to processing an incoming UWB signal in two different bands in parallel and thereafter summing their respective magnitudes.
Ultra-wideband (UWB) communication systems employ very short pulses of electromagnetic radiation or impulses with short rise and fall times which results in a spectrum with a very wide bandwidth. UWB communications have a number of advantages over conventional systems. The very large bandwidth for instance facilitates very high data rate communications. Since ultra short pulses of radiation are employed, the average transmit power may be kept low even though the power in each pulse is relatively large. Since the power in each pulse is spread over a large bandwidth, the power per unit frequency may be very low, allowing UWB systems to coexist with other spectrum users and providing a low probably of intercept. UWB techniques are attractive for short range wireless devices, such as radio frequency identification (RFID) systems, because they allow devices to exchange information at relatively high data rates. For instance, an Ultra Wideband Radio Frequency Identification Technique system may be seen in the Reunamaki U.S. Pat. No. 7,733,229. In this invention, UWB techniques are applied to RFID in which a reader generates a UWB IR interrogation signal and receives a UWB IR reply signal from an RFID tag in response to the interrogation signal.
Federal Communications Commission (FCC) defines a UWB pulse as one whose 10 dB bandwidth either is at least 500 MHz or whose fractional bandwidth is greater than 0.20. The 500 MHz minimum bandwidth limit sets a threshold at 2.5 GHz. Below this 2.5 GHz threshold, signals are considered UWB if their fractional bandwidth exceeds 0.20, while above the threshold signals are UWB if their bandwidth exceeds 500 MHz. Fractional bandwidth is defined as the ratio of the 10 dB bandwidth to the center frequency. For example, a 500 MHz 10 dB bandwidth UWB signal centered at 6 GHz has a fractional bandwidth of 0.083 ( 500/6000). For UWB whose center frequency is greater than 2.5 GHz, the 500 MHz 10 dB analog bandwidth needs to be processed.
In our past U.S. patent application Ser. No. 12/387,425; filed May 1, 2009, for Pulse-Level Interleaving for UWB Systems, a UWB transmitter transmits a multi-pulse per bit signal to a UWB receiver for multi-bit processing. A bit stream is transmitted using a plurality of UWB pulses for each bit frame. The pulse level interleaving of the pulses is accomplished prior to transmission of the signals by a plurality of UWB transmitters operating at the same time. The receiver de-interleaves the pulses and then aggregates the energy from the multiple pulses within each frame.
In order to realize the full gain of a 500 MHz analog bandwidth signal, data must be processed digitally at a rate of 1000 Msps. Unfortunately, 1000 Msps (or 500 Complex Msps→500 MHz complex digital bandwidth) is difficult to implement with most Field programmable gate arrays (FPGA). Therefore, a smaller digital bandwidth is used, which results in loss of signal strength.Loss(dB)=10×log10(Analog Bandwidth/Complex Digital Bandwidth)
For example, an FPGA running at 320 Complex Msps can process only 320 MHz of analog bandwidth; therefore, if the received signal has 500 MHz of analog bandwidth, 1.94 dB is lost in FPGA digital implementation.Loss(dB)=10×log10(320 Msps/500 MHz)−)1.94 dB
Range is a vital objective of any communications link, particularly in UWB asset tracking systems. The greater the net gain in a link budget, the greater the range. FCC imposes a power limit on UWB transmitters. Transmit power cannot be increased, unless bandwidth of the pulse is also increased proportionately. Therefore, in order to add gain to the link to maximize the range, while keeping the transmitter power and pulse repetition interval fixed, the receiver must process the entire bandwidth, thereby minimizing digital implementation loss and promoting higher range. The present invention processes nearly the entire bandwidth and minimizes digital implementation loss and promotes a higher range.
The present invention processes a UWB incoming signal in two different signal bands in parallel and then sums their magnitudes to facilitate the Field programmable gate array (FPGA) processing of the entire UWB bandwidth to thereby minimize digital implementation loss and promote a higher range.